The present invention is directed to a method of selecting and implementing threshold techniques for a Bio-Sensor.RTM. (a water quality monitoring system manufactured by Biological Monitoring, Inc. (BMI)) in which the threshold of a signal-filtering process is selected. The Bio-Sensor.RTM. is used, for example, in a system which detects the ventilatory frequency of fish used as biological sensors, for example, in a water quality monitoring system. The water quality monitoring system is described in U.S. Pat. No. 5,140,855, filed Nov. 13, 1990, U.S. Pat. No. 5,140,855 to Gruber et al., incorporated by reference herein. In addition, a Bio-Amp.RTM. employed in the system is described in U.S. Ser. No. 07/611,664, filed Nov. 13, 1990, now abandoned, by Harrison et al., incorporated by reference herein. The method of the present invention selects and implements different waveform processing techniques employing computer software developed to adequately process incoming signals.